Sound proofing materials and structures have important applications in the acoustic industry. Traditional materials used in the industry, such as absorbers, reflectors and barriers, are usually active over a broad range of frequencies without providing frequency selective sound control. Active noise cancellation equipment allows for frequency selective sound attenuation, but it is typically most effective in confined spaces and requires the investment in, and operation of, electronic equipment to provide power and control.
Phononic crystals, i.e. periodic inhomogeneous media, have been used as sound barriers with acoustic passbands and band gaps. For example, periodic arrays of copper tubes in air, periodic arrays of composite elements having high density centers covered in soft elastic materials, and periodic arrays of water in air have been used to create sound barriers with frequency-selective characteristics. However, these approaches typically suffer from drawbacks such as producing narrow band gaps or band gaps at frequencies too high for audio applications, and/or requiring bulky physical structures.
There is thus a need for improved sound barriers with diminished drawback of the traditional technologies.